This invention relates to bus drivers operating with three state outputs and to logic systems in which a plurality of such bus drivers are selectively enabled to drive a common bus.
In such logic systems there always exists the possibility that more than one driver might be driving the same bus simultaneously and that they might be driving against each other. In that event, one of the output transistors in a low impedance state could be subjected to current overload sufficient to cause it to burn out.
In order to minimize the probability of simultaneous bus drive by more than one driver, it is common to employ very precise timing circuits. However, even when the drivers are under precise timing control, there still exists the possibility of accidental short circuits that may be caused by defective wiring or device failure.